Buckling Analysis And Optimization Design For Piles Foundation With High Bridge Piers

With the exploitation of west china and the development of infrastructural construction such as highway traffic in remote mountainous area, it's inevitable to build many viaducts to cross rivers and valleys. And the rational design of pile foundation with high bridge pier is an important technical problem on the basis of understanding the structure characteristics of bearing mechanics, deformation and stability. Under the supports of the program of National Natural Science Foundation "study on the buckling mechanism for pile foundation with high pile-cap based on meshless method"(50378036) and the scientific project of Communications Department of Hunan Province "study on the bearing mechanism and optimization design for piles foundation with high bridge piers in mountainous district"(200513), this dissertation researches the bearing and buckling mechanics of pile foundation with high bridge pier from severals aspects of theoretical analysis, numerical simulation and model experiment.At first, buckling mechanic of piles foundation with high bridge piers is discussed in detail. Bridge pier and pile foundation are analyzed as a whole for the firs time and a simplified calculation model of pile foundation with high bridge pier is proposed, in which the influence of pier-pile stiffness and surrounding soil body may be considered. Using energy method the theoretical solutions of critical buckling load and effective length are obtained for different boundary condition of bridge construction stage and working stage. Correlative effect factor analyses show that surrounding soil and pile depth embedded in soil have significant impact on buckling performance, and that structural stiffness enhancement can not obviously improve pier-pile stability because structure buckling failure is not material failure. And soil condition around the piles is benefit for foundation stability in some range under ground. There may be exists an effective depth in piles.Then from the angle of solid mechanics large deformation in structure is discussed for further understanding of buckling character. And the calculation formulas of large deformation of meshless method are derived. Based on full Lagrangian method approximate function on initial configurations is constructed and equilibrium equations are obtained. Equation group of nonlinear meshless method is solved by arc-length method. Uniform experiment design is introduced to arrange the node position equably in domains of calculation points in order to avoid matrix singularity and to alleviate computational burden.And then the laboratory buckling model experiments of piles foundation with high bridge piers are self-designed. Taking into account of the effect factors of pier-pile length ratio, boundary condition and material stiffness, buckling failure mechanism of piles foundation with high bridge piers are gained. The experimental measured values of buckling load and horizontal displacement at the top of piers are in agreement with the calculated results based on numerical analyses of meshless method. So the accuracy of the computer program of meshless method is verified. It is indicated that meshless method developed in this dissertation may be applied effectively to the buckling analysis of piles foundation with high bridge piers. Furthermore, buckling effect factors and their influence law are exploited.Finally, combining the character of piles foundation with high bridge piers with engineering practice, four optimal mathematic models are proposed and flow diagram of optimization analysis is fulfilled by the computer optimum program. A numerical example is analyzed to get optimal solution by using this program. Meanwhile based on the optimal model with buckling coefficient as the objective function, parameter variables are discussed about their effect rule toward the optimal value of objective function.